For Ford Street Rod Small Block 289-302-351 4-1 Design 2-PC Stainless Steel Exhaust Header/Manifold Made of high quality steel with 2 x 4-1 direct bolt-on design TIG welded CNC machine flange Metal gasket included / Inlet: 1.33" / Outlet: 2.37" Increase high flow air, instantly gain 10 to 15 Hp. / Tq Does not work with stock clutch linkage